Also in Delaware County, a student's infection led officials to close Indian Lane Elementary near Media yesterday, locking the doors while janitors attacked buildings with mops and disinfectants.

Across the country, dozens of reported cases suggested an epidemic of an infection few had heard much about - MRSA, for methicillin-resistant Staphylococcus aureus.

Yet scientists say the MRSA problem is no worse now than it was last week, or even last year.

People are on high alert to the threat of MRSA after the infection killed a Virginia high school student Monday and news outlets reported a rise in a new strain of the bacteria two days later.

The disease usually infects through a skin lesion and is only rarely fatal. Doctors say the public may be misled by the term antibiotic resistant. MRSA is a staph bacterium that evolved a resistance to penicillin, its synthetic counterpart methicillin, and several related antibiotics. But it can be cured with many other antibiotics, so most cases clear up with the right treatment.

"It's an inappropriate panic," said Susan Coffin, director of infection prevention and control at Children's Hospital of Philadelphia. "I'm getting letters from people saying their children are told not to return to school" after an infection.

Scientists say MRSA represents a long-term problem rather than an immediate threat.

In recent years, a number of isolated cases and outbreaks have cropped up among professional football teams and high school athletes, said Neil Fishman, an infectious-disease specialist at the University of Pennsylvania Medical Center.

Usually the infection is transmitted from skin-to-skin contact, abrasions, and possibly the sharing of razors, towels and soap. The infections typically fall under the radar, the students get treatment, and nobody worries.

That all changed this week.

On the heels of the Virginia death, the Centers for Disease Control and Prevention issued a report that said a relatively new strain of MRSA accounted for about 14 percent of the more dangerous invasive cases.

On Wednesday, the Washington Post reported that annual MRSA deaths from all strains now outnumber deaths from AIDS.

That's misleading, Fishman said, because most of those MRSA deaths happen to terminally ill or very frail people in hospitals where it is not always clear the death was really due to MRSA. And many other diseases kill more people than AIDS.

Ed Cardow, the Chichester school board vice president, said the superintendent contacted the state Health Department and the CDC immediately after a MRSA case was reported. Cardow said the superintendent then followed their recommendations to clean overnight with a bleach and water solution and reopen in the morning.

"We jumped on it as fast as we could," Cardow said.

In New Jersey, Point Pleasant Boro High School was being disinfected by Aramark cleaning crews with hospital-grade sanitizing equipment after one student was found to have MRSA.

The middle and elementary schools will be cleaned this weekend.

Yet experts agreed that disinfecting school buildings is unlikely to help.

"In general we do not recommend closing schools and cleaning them," said Arjun Srinivasan, a medical epidemiologist at the CDC. "It's not necessary to go to such extremes to prevent the spread of MRSA. The transmission is predominantly through skin-to-skin contact or by a surface that previously contacted an open lesion."